PDAC is the most frequent pancreatic carcinoma and is the fourth cause of death in United States and Europe. Most of the patients die within twelve months and the survival percentage at five years from diagnosis is 2%. Pancreatectomy remains the main treatment for PDAC, but the benefits thereof are restricted to 20% of the cases in which diagnosis was made at an early stage. Despite the improvements occurred in medical and surgical treatments, including the use of monoclonal antibodies, vaccines and chemotherapy, very few biomarkers are hitherto available for PDAC diagnosis and prognosis, which on top of that are poorly reliable. The most used serological PDAC biomarker is the sialylated antigen from the Lewis blood group CA19.9, which is mainly used for monitoring the response to therapy. This antigen can effectively be present at high concentrations even in the serum of patients with benign pancreatic diseases, such as chronic pancreatitis and biliary obstruction, which results in false positives. Furthermore, this antigen is not expressed in 5-10% of the population and therefore is not suitable to be used in all PDAC patients.
For these reasons, alternative biomarkers for diagnosing PDAC are under examination. Identifying a biomarker that is reliable and usable in a high percentage of patients would allow to decrease the use of invasive procedures, such as biopsy collections and histopathologic examinations. A biomarker with these features could also be used for identifying and assessing novel drug candidates for PDAC treatment.
Large-scale analysis for protein and RNA expression is among the recently used technologies for identifying potential PDAC biomarkers. In particular, proteomic technologies have been used to identify antigens capable of inducing an antibody response in PDAC patients. This has been done by analysing protein profiles separated by two-dimensional electrophoresis (2-DE), recognised by serum from PDAC patients and subsequently identified by mass spectrometry. By characterising the B cell repertoire against antigens specifically expressed by tumour cells (the so-called Immunoma of human cancer), it may be possible to define specific targets that are involved in tumour immuno-survey and immuno-editing and understand the mechanisms responsible for uncontrolled cell proliferation and metastases.
Certain authors suggested that immunotherapy may be a practicable approach for pancreatic cancer. Actually, PDAC-specific protein lists have been generated on the basis of their high expression at the RNA level (WO2004/055519), or on the basis of large-scale proteomic or serological-proteomic analyses, by using sera from PDAC patients. However, as far as the inventors know, none of these proteins has been concretely proven useful as a specific diagnostic reagent for PDAC.
In the International Patent Application WO 2008037792, the existence of six different phosphorylated human alpha-enolase isoforms (ENOA1-6) is reported and the use of one of these isoforms, phosphorylated at least in three positions, is claimed for PDAC diagnosis. The description of WO2008037792 shows experimental data concerning the analysis of the phosphorylation of the ENOA3 isoform, but this isoform is actually not related to PDAC. By contrast, the isoforms ENOA1 and ENOA2—related to PDAC—have not been sufficiently characterised in structural terms and no unequivocal criterion is provided in order to distinguish them from non-PDAC related isoforms.
Therefore, a need remains to detect and characterise a biomarker that is specific and reliable for early PDAC diagnosis, designed to distinguish this serious tumour pathology from other pathologies.